Safety pilot control system



E938. L. KUEMPEL SAFETY PILOT CONTRQL SYSTEM Filed March 4, 1935SHAW/14M Le0nL.Kiempel GUM;

Patented Dec. 27, 1938 PATENT OFFICE SAFETY PILOT CONTROL SYSTEM Leon L.Kuempel, Minneapolis, Minn., assignor to Minneapolis-Honeywell RegulatorCompany, Minneapolis, Minn., a corporation of Delaware Application March4,

2 Claims.

This invention relates to a safety pilot control system.

It is an object of this invention to provide a system for a devicehaving a main burner and a 5 pilot burner for igniting the main burner,comprising a valve for controlling the main burner, means for operatingthe valve, control means including a thermostat for the valve,electrodes adapted to be bridged by the pilot flame, and 10 choke meansconnected between the electrodes and control means to permit operationof the valve operating means under the command of the thermostat whenthe pilot flame bridges the electrodes.

Another object of this invention is to provide a control system for amain burner and a pilot burner wherein the control system comprises,

means for controlling the main burner including a relay, choke means forcontrolling the opera- 20 tion of the relay, and means associated withthe pilot flame for controlling the choke meansto open the relay uponpilot flame failure.

A further object is to provide a yste'm for controlling an electricmotor comp sing, a relay having a coil and a load switch operatedthereby, a load circuit including the electric motor and the loadswitch, choke means, a circuit including the choke means and the coil,and means for decreasing the impedance of the choke means to energizethe coil and permit operation of the motor.

More specifically, it is an object of this invention to provide acontrol system for a main burner and a pilot burner, the systemcomprising a valve for controlling the supply of fuel to the mainburner, an electric motor for opening the valve upon energizationthereof, a thermostatic switch, a relay having a coil and load switchoperated thereby, a load circuit including the motor, the thermostaticswitch and the load switch, a step-up transformer having a primary and asecondary, a primary circuit including the primary of the transformerand the relay coil and electrodes adjacent to the pilot burner adaptedto be bridged by the pilot flame and connected to the secondary of thetransformer whereby the primary circuit is energized when the electrodesarebridged by the pilot flame to close the load switch and permitenergization of the motor when the thermostatic switch closes.

Other objects and advantages will become apparent to those skilled inthe art by reference,

to the accompanying specification, claims and drawing in which drawingthere is diagrammatically disclosed the preferred form of my 5invention.

1935, Serial No. 9,208

Although my control system may be applied-to any type of system, it isshown for purposes of.

illustration as applied to a heating system wherein a warm air furnaceis designated at In. The furnace I is provided with a bonnet I I havingducts I2 emanating therefrom for delivering warm air to spaces to beheated. Located in the furnace I0 is a combustion device which may takethe form of a burner l3. Expanded gases of combustion are taken from thefurnace l0 by means of a flue or duct M which leads to the usual stack(not shown).

A pipe l5 leading from some source of fuel supply terminates in a valvel6 and a pipe l1 leads from the valve 16 to the burner l3 whereby fuelis supplied to the burner l3 under the control of the'valve I6. Locatedadjacent the burner l3, so that'the burner I3 may be ignited thereby,

is a pilot burner l8. Fuel is always supplied to the pilot burner It! bymeans of a pipe I9 con- 20 nected into the pipe l5 ahead ofthe valve l6.The valve I6 is operated by means of a valve motor having a lever 2|pivoted at 22. A collar 23 is secured to a valve stem 24 of the valve [6and is held against the upper surface of the lever 25 2| by means of aspring 25 abutting against a support 26. Pivoted intermediate the endsof the lever 2| is a hooked arm 2! which is adapted to be engaged by apin 28 located on a gear 29. The gear 29 is rotated by means of apinion30 30 which is in turn secured to the gear 3|. The gear 3| isrotated by means of a motor pinion 32 which is secured to the motorrotor 33. Themotor has a field diagrammatically shown at 34 and uponenergization of field 34, the rotor 33 is 35 placed in operation tocause clockwise rotation of the gear 29 whereby the pin 28 engages inthe hooked portion of the arm 21 to move the lever 21 in acounter-clockwise direction about its pivot 22, This movement of thelever 2| causes upward movement of the valve stem 24 against the actionvof spring 25 to open the valve Hi. When the valve I6 is completelyopened, further movement thereof is prevented and the motor becomesstalled in this position. As long as the field 34 remains energized, thevalve IE will remain in the open position. When the field 34 isdeenergized, the spring 25 causes closing of the valve l6 and consequentreverse rotation of the gear train and motor rotor 33.

Power is supplied to the control system of my invention by means of linewires 35 and 36. A wire 31 connects the line wire 35 to one end of aprimary 38 of a step-up transformer 39, preferably of the power type,which has a secondary 49. The other end of the primary 36 of thetransformer 39 is connected by means of a wire 4| to one end of a relaycoil 42. The other end of the relay coil 42 is connected by means of awire 48 to the line wire 36. The secondary 49 of the transformer 39 isconnected to electrodes 65 and 66 which are located in the pilot flameof the pilot burner l8.

As is known in the art, a power type transformer places a high impedancein the primary thereof when the secondary thereof is in open. circuitposition so that substantially no current is allowed to pass through theprimary. However, when the secondary of such a transformer is shorted,the impedance of the primary is greatly reduced to permit a largecurrent flow therethrough. From this it is seen that such a transformerforms a very good choke device which prevents substantially the flow ofcurrent through a circuit and which, under certain conditions, allowsthe flow of a large current through the circuit.

It is also known in the art that flame conducts electricity much betterthan air. This principle is used in my invention to complete a circuitthrough the secondary of the step-up transformer 39 to, in efiect,short-circuit the secondary thereof to permit a large flow of currentthrough the primary 38.

Since the relay coil 42 is located in series with the primary 38 of thepower type transformer 39, burning out of the transformer 39 is therebyprevented when the secondary 49 is short-circuitedby reason of the pilotflame bridging the two electrodes 65 and 66.

From the above discussion, the operation of this portion of theinvention becomes self-evident, it being sufficient to state that whenthe pilot flame bridges the electrodes 65 and 66, the relay coil 42becomes energized by reason of the flow of current from line wire 35through wire 31, primary 38, wire 4|, relay coil 42 and wire 43 back toline wire 36. When the pilot flame becomes extinguished, the impedancein the coil 38 is greatly increased which will prevent flow of currentthrough the above circuit and cause deenergization of the relay coil 42.

A' step-down transformer is indicated at 45 and comprises a primary 44and a secondary 46. The primary 44 is connected to some source of powerand for purposes of convenience, it is shown as connected across thewires 43 and 31. A condition responsive means which may take the form ofa thermostat 41 responsive to space temperature, has contacts 48 and 49contained thereon. These contacts 48 and 49 are adapted to sequentiallyengage contacts '59 and respectively since the distance between contacts48 and 59 is less than the distance between contacts 49 and 5|. Thethermostat 41 is held in place by means of a binding post 52. Thebinding post 52 is connected by means of a wire 53 to an electrodelocated in a mercury switch 44 which in turn is secured to the lever 2|by means of a bracket 55. The other electrode of the mercury switch 54is connected by means of a wire 56 and a wire 51 to the contact 5|. Thecontact 59 is connected by means of a wire 58 to one end of thesecondary 46 of the step-down transformer 45. The other end of thesecondary 46 is connected by means of a wire 59, to a contact 69. Switcharm 6| which is operated by the relay coil 42 is connected by means of awire 62 to the field 34 of the valve motor. The other end of the field34 is connected by means of a wire 63 to the Junction of wires 69 and61. The switch arm 6| is normally urged away from the contact 69 bymeans of gravity or springs or like mechanisms. The contact 99 and theswitch arm 6| form a load switch operated by the relay coil 42. The loadswitch and the relay coil form a relay of the usual design.

Upon a decrease in temperature affecting the thermostat 41, contact 49is first moved into engagement with contact 59 and upon a furtherdecrease in temperature contact 49 is moved into engagement with contact5| to complete a starting circuit from the secondary 46 through wire 58,contacts 59, 48, 49 and 5|, wire 51, wire 63, field 34, wire 62, switcharm 6|, contact 69 and wire 59 back to the secondary 46. Completion ofthis circuit causes rotation of the rotor 33 and consequent raising oflever 2| and opening of the valve l6. When the valve I6 is opened andthe lever 2| is moved to its upper position, the mercury in the mercuryswitch 54 bridges the con tacts contained therein and completes aholding circuit from secondary 46 through wire 58, contacts 59 and 48,thermostat 41, binding post 52, wire 53, mercury switch 54, wire 56,wire 63, fleld 34, wire 62, switch arm 6|, contact 69 and wire 59 backto the secondary 46. The motor will remain energized and the valve l6will be held in the open position until an increase in temperaturecauses the thermostat 4! to move the contact 48 away from the contact 59whereby the above holding circuit will be broken and the spring 25 willmove the valve l6 to closed position.

The above operation has been set forth upon the assumption that switcharm 6| is in engagement with contact 69. The switch arm 6| is held inengagement with the contact 69 when the relay coil 42 is energized andas pointed out above, the relay coil '42 is energized and the switch arm6| is held in engagement with the contact 69 only when the pilot flamebridges the electrodes 65 and 66. From this it is seen that only whenthe pilot flame bridges the electrodes 65 and 66, the motor for openingthe valve l6 may be energized under the command of the conditionresponsive device 41. However, if the pilot flame becomes extinguished,the switch arm 6| will be moved out of engagement with the contact 69and the motor may not be energized to open the valve l6 even though thethermostat 41 should be calling for heat.

From the above it is seen that I have provided a safety pilot controlsystem wherein it is impossible to open the control valve to the mainburner if the pilot burner should be extinguished thereby preventing theaccumulation of large amounts of combustible gases within the furnacel9. However, in my system, if the pilot flame is burning properly andbridges the electrodes 65 and 66, the valve I6 is opened and closedunder the direct command of the condition responsive means or thermostat41. Further, since the valve I6 is closed by means of a spring, powerfailure protection is also provided in my system since upon the failureof power in the lines 35 and 36 it will be impossible to open ormaintain open the valve |6.

While one embodiment of the present invention has been shown anddescribed in detail, many modifications will occur to those skilled inthe art. It is intended in this application to cover all suchmodifications as fall within the scope of this invention as defined bythe appended claims.

I claim as my invention:

1. In a system of the class described, a main burner, a pilot burner forigniting said main burner, a valve for controlling the supply of fuel tosaid main burner, an electric motor for opening said valve uponenergization thereof, a thermostatic switch, a relay having a coil and aload switch operated thereby, a source of power, a load circuitincluding the source of power, the motor, the thermostatic switch andthe load switch, a stepup transformer having a primary and a secondary,a primary circuit including the source of power, said primary of thetransformer and said relay coil, and electrodes adjacent the pilotburner positioned to be bridged by the pilot flame and connected to thesecondary of the transformer whereby the primary circuit is energizedwhen the electrodes are bridged by the pilot flame to close the loadswitch and permit energization of the motor when the thermostatic switchcloses, said electrodes being so spaced relative to the voltage of saidsecondary that in the absence of flame no current passes therebetween.

2. In a system of the class described, a main burner, a constantlyburning pilot burner for igniting said main burner, a valve forcontrolling the supply of fuel to said main burner, an electricallycontrolled motor for opening said valve upon energization thereof, athermostatic switch, a relay having a coil and a load switch operatedthereby; a source of power; a load circuit including the source ofpower, the motor, the thermostatic switch and the load switch, a step-uptransformer having a primary and a secondary, a continuously closedprimary circuit including the source of power, said primary of thetransformer and said relay coil; and electrodes adjacent the pilotburner positioned to be bridged by the pilot flame and connected to thesecondary of the transformer whereby the primary circuit is maintainedenergized so long as the electrodes are bridged by the pilot flame tomaintain the load switch closed and permit energlzation of the motorwhen the thermostatic switch closes, said electrodes being so spacedrelative to the voltage of said secondary that in the absence of flameno current passes therebetween.

LEON L. KUEMPEL.

